1. Field of the Invention
This invention relates to a method of washing filters that continuously remove magnetic particles, produced by metal processing or wear, that are present in water and in the atmosphere, and also removing microorganisms accompanying magnetism and magnetic particles entrained in fluids.
2. Description of the Prior Art
Magnetic separators employing permanent magnets and electromagnetic or permanent magnetic filters employing ferromagnetic fibers or beads are conventionally used to remove magnetic particles and microorganisms accompanying magnetism entrained in fluids (hereinafter the removal of magnetic particles and the like adhering to electromagnetic filters will also be referred to as "washing").
However, magnetic separators have a poor performance and provide insufficient washing. Electromagnetic filters, on the other hand, have superior magnetic-particle-removal performance but it is necessary to clean the filters effectively. In JP-A-54(1979)-86878, for example, in which a ferroelectromagnet is used to set the magnetic field to zero, a large apparatus is required to free the filter from the magnetic field, involving a large consumption of electricity and a major outlay in manufacturing costs that make the cost-performance thereof unsatisfactory.
Washing water, hydraulic fluid, cooling water, process fluids and other such fluids used in product manufacturing processes in the steel industry, automotive pressed parts and processing industries, for example, contain large quantities of magnetic particles entrained therein. As well as reducing the surface cleanliness of the products, this has a major effect on product quality, producing blemishes and the like, and also because of these magnetic particles, washing tanks and piping has become very costly.
In fresh-water and waterworks treatment facilities also, the formation of rust, iron bacteria and the like from tanks and pipes is unavoidable and is a cause of scale-containing waste water and the like in the waterworks system. Large purification tanks and separation equipment are required to remove this at a huge cost.
Thus, for manufacturing industries, the efficient removal of magnetic particles in such fluids is beneficial in terms of product quality and equipment maintenance costs, and for water treatment facilities it also helps to reduce the equipment costs and to make the water supply safer. However, because such magnetic particles are so small, ordinary filters are quickly clogged, and the cost-performance of conventional magnetic separation apparatuses renders them unsuitable.
In the example of the steel-making industry, minute steel particles produced during the cold-rolling of steel sheet adhere to the sheet. The sheet is therefore subjected to a process to remove the particles, for example, an electric cleaning process, before it is sent on to be heat-treated, plated, and so forth.
Drum-type magnetic separators and cloth filters are generally used to reduce the amount of steel dust in the tanks of rolling oils and washing fluids. However, drum-type magnetic separators have a very low removal efficiency, because the magnetic particles are only held by the magnetic force in the vicinity of the surface of the drum. With cloth filters, too, the minute size of the steel particles makes the removal efficiency lower, in addition to which the filters quickly become clogged, involving large outlays for cloth.
Conventional apparatus include electromagnetic filters that employ ferromagnetic small-gauge wire. Utilizing the principle of high-gradient magnetic separation, a large magnetic gradient is generated around the ferromagnetic small-gauge wires to effect separation of the magnetic particles with good efficiency. However, with current constructions it is difficult to clean the filters. In the cleaning process huge electromagnetic coils are used to control the magnetic field, so the cleaning involves the use of a large apparatus, major fabrication expenditures and the consumption of enormous amounts of electricity. Therefore the major problem is how to remove the magnetic particles adhering to the filters economically and efficiently.
There are apparatuses that combine the low cost of the magnetic separator with the high efficiency of the electromagnetic filter, but the washing efficiency of such apparatuses is poor and high efficiency cannot be maintained over a long period.